1. Field of the Invention
The field of the present invention is pressure equalization mechanisms for plumbing, disposal, and waste systems.
2. Background
The plumbing, disposal, and waste system (PDWS) of most residential and commercial buildings, such as those associated with sinks, bathtubs, and toilets, require mechanisms to equalize pressure between the PDWS and the ambient atmosphere when the pressure in the PDWS is less than atmospheric pressure. Pressure equalization is necessary to maintain the liquid trap seal employed in the most common PDWS.
Traditionally, external ventilation stacks have been used to vent the PDWS to building exteriors, thereby allowing the pressure within a PDWS to constantly equalize to atmospheric pressure. More recently, air admittance vents (AAV) have replaced ventilation stacks. AAVs allow air to enter the PDWS and restrict air from flowing out of the PDWS. By restricting flow (which may include air, gases, and liquid waste) out of the PDWS, an AAV may be placed most anywhere within a building while still preventing negative pressure, i.e., less than atmospheric pressure, to build up within the PDWS.
In order to achieve the desired functionality, an AAV requires a valve that can be responsive to small drops in pressure (less than 1/100 PSI) below atmospheric pressure. The valve also needs to be able to create a good seal in response to small increases in pressure within PDWS being regulated. Finally, the preferred AAV will have a wide range of operating temperatures and will be inert to chemicals that are commonly found in a PDWS, most especially methane gas and water vapor.